This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 11-183469, filed Jun. 29, 1999; and No. 2000-033504, filed Feb. 10, 2000, the entire contents of which are incorporated herein by reference.
The present invention relates to a drying apparatus and a drying method for drying to-be-dried objects, such as cleaned wafers of semiconductors, substrates for liquid crystal displays, substrates for recording disks, substrates for masking, and other substrates.
Generally known are drying apparatuses for drying to-be-dried objects such as semiconductor wafers that are subjected to a cleaning process, rinse process, etc. As a typical drying apparatus, there is a so-called vapor drying apparatus that uses a vapor of an organic solvent. In the vapor drying apparatus, the organic solvent on the surface of a to-be-dried object is evaporated in a short time after a treatment liquid, such as pure water, adhering to the object surface is replaced with the organic solvent.
The vapor drying apparatus comprises an apparatus body that constitutes its outer hull, a support mechanism for supporting a wafer, a liquid recovery section, etc. The apparatus body is provided with a drying vessel that is stored with the organic solvent. Isopropyl alcohol (IPA) is used as an example of the organic solvent. A heating device is provided at the bottom of the drying vessel. The heating device produces an organic solvent vapor by heating the organic solvent. The support mechanism has a function to load into or unload the wafer, as an example of the to-be-dried object, from the drying vessel and to support the wafer in the drying vessel. The liquid recovery section discharges the treatment liquid (e.g., pure water), which flows down from the surface the wafer, to the outside of the apparatus.
Before the wafer is loaded into the drying vessel, it is cleaned with a cleaning fluid, such as hydrogen fluoride or pure water, in the cleaning process. The wafer is rinsed with the treatment liquid, such as pure water, in the rinse process after the cleaning process. Before it is inserted into the drying vessel, therefore, the wafer has the treatment liquid on its surface.
The wafer, having the treatment liquid such as pure water thereon, is inserted into the drying vessel by means of the support mechanism, and exposed to the vapor of the organic solvent such as IPA. The vapor is condensed on the surface of the wafer, and the organic solvent adheres to the wafer surface. The treatment liquid having so far been adhering to the wafer surface flows down by being replaced with the organic solvent, and is recovered by means of the liquid recovery section. The organic solvent on the wafer surface is evaporated in a short time, whereupon the wafer is dried. As the treatment liquid flows down from the surface of the wafer, particles on the wafer surface flows down together with the liquid.
If the treatment liquid contains particles in the rinse process, the particles sometimes may adhere to the rinsed wafer surface. If the wafer having the particles thereon is treated by means of the vapor drying apparatus, the particles on the wafer surface may possibly flow down together with the cleaning fluid and unfavorably remain in the drying vessel.
The wafer rinsed with the treatment liquid, e.g., pure water, is at a low temperature immediately after it is inserted into the drying vessel. Therefore, the vapor in the drying vessel is rapidly reduced as the organic solvent is quickly condensed in plenty on the wafer surface immediately after the wafer is loaded into the drying vessel. If the vapor quantity is reduced, a part of the wafer may possibly be exposed to air. Since the heating device goes on heating the organic solvent, the organic solvent vapor continues to be produced. In some cases, however, it takes scores of seconds, for example, to allow the wafer to be covered entire again.
A part of the wafer is left to dry naturally before the wafer is covered entire with the vapor. As this is done, natural oxide films or spots called watermarks inevitably develop along the respective contours of drops of the treatment liquid having been adhering to the wafer. In the case where the wafer is cleaned with hydrogen fluoride or the like in the cleaning process, in particular, the surface of the wafer is hydrophobic and activated, so that watermarks are liable to develop.
Immediately after the wafer is inserted into the drying vessel, as mentioned before, a relatively large quantity of the organic solvent is condensed in a moment on the wafer surface. Accordingly, the organic solvent should never fail to be heated in plenty to produce the vapor, so that a drying process entails high cost. Further, the conventional vapor drying apparatus requires use of a large quantity of organic solvent vapor in the drying process. In drying a large-diameter wafer, therefore, it is hard to secure sufficient organic solvent vapor to be replaced with pure water on the wafer.
Accordingly, a first object of the present invention is to provide a drying apparatus capable of securely removing particles from the surface of a to-be-dried object, such as a wafer, and preventing watermarks from developing on the surface of the to-be-dried object. A second object of the invention is to provide a drying apparatus capable of lowering the cost of a drying process.
In order to achieve the first object described above, a drying apparatus according to the present invention comprises a drying vessel for storing a to-be-dried object, a treatment liquid feeder-discharger capable of feeding a treatment liquid into the drying vessel and discharging the treatment liquid in the drying vessel from the bottom side thereof, a heated organic solvent supplier for feeding a heated organic solvent onto the treatment liquid in the drying vessel, and a vapor supplier for feeding an organic solvent vapor into the drying vessel. Preferably, the treatment liquid feeder-discharger includes an inlet-outlet port opening in the base portion of the drying vessel, an inlet-outlet pipe connected to the inlet-outlet port, a valve, and a treatment liquid source.
In the drying apparatus of the invention, the interior of the drying vessel can be cleaned by feeding the treatment liquid such as pure water into the drying vessel by means of treatment liquid feeder-discharger and causing the pure water to overflow the top of the drying vessel. Particles can be removed from the drying vessel as the treatment liquid is discharged from the base portion of the drying vessel after the vessel is cleaned. The space over the treatment liquid in the drying vessel is filled with the vapor. The to-be-dried object is immersed in the treatment liquid. The organic solvent is condensed on the surface of the object as the object is exposed above the level of the treatment liquid. In this case, at least the lower part of the to-be-dried object is immersed in the treatment liquid before the organic solvent is condensed over the whole surface of the object, so that the temperature of the object is kept lower than that of the vapor. Thus, the organic solvent can be securely condensed on the whole surface of the object.
The drying apparatus of the invention may comprise a first inert gas supplier for introducing an inert gas into the drying vessel through the top portion thereof. Since this inert gas supplier feeds an inert gas such as nitrogen into the drying vessel, the space over the treatment liquid is filled with the organic solvent vapor and the inert gas. Since the to-be-dried object in the drying vessel is covered with the inert gas, in this case, it is restrained from touch oxygen, so that watermarks can be restrained from developing on the surface of the to-be-dried object.
In the drying apparatus of the invention, moreover, the vapor supplier may include an organic solvent tank for storing the organic solvent, heating means for heating the organic solvent in the organic solvent tank, thereby producing the organic solvent vapor, and a communicating section for feeding the organic solvent vapor in the organic solvent tank onto the treatment liquid through the top portion of the drying vessel. Further, the drying apparatus may comprise means for introducing the organic solvent heated outside the drying vessel into the organic solvent tank, in order to produce the organic solvent vapor.
For example, the heated organic solvent supplier includes a heater for heating the organic solvent, discharge means for discharging the heated organic solvent toward the treatment liquid through the top portion of the drying vessel, and organic solvent diffusing means for uniformly supplying the heated organic solvent from the discharge means to the whole level of the treatment liquid in the drying vessel, thereby forming a film of the organic solvent on the liquid level.
The drying apparatus of the invention uses pure water of, e.g., normal temperature (about 20xc2x0 C.) as the treatment liquid. The organic solvent (50 to 150 cc of a liquid of 60 to 80xc2x0 C.) heated in any other place than the drying vessel is discharged toward the treatment liquid level by means of the discharge means of the heated organic solvent supplier. The discharged heated organic solvent is uniformly diffused to the whole treatment liquid level by means of the diffusing means, whereupon a stable film of the organic solvent is formed on the treatment liquid level.
As the to-be-dried object immersed in the treatment liquid emerges from the treatment liquid, some of the organic solvent that forms the organic solvent film adheres uniformly and continuously to the surface of the to-be-dried object. The treatment liquid having so far been adhering to the surface of the to-be-dried object is replaced with the organic solvent and flows down. In order to form the organic solvent film on the treatment liquid level, it is necessary to give a temperature difference not smaller than a predetermined value between the treatment liquid and the organic solvent to be fed onto the treatment liquid and to feed rapidly the organic solvent in a given or larger quantity. The following is a description of the reason for this requirement.
When the organic solvent is supplied to the treatment liquid level, the treatment liquid and the solvent are mixed to form the organic solvent film. The surface tension of the organic solvent film is lower than that of a treatment liquid level that contains no organic solvent. Accordingly, the surface tension between the organic solvent film and the treatment liquid level has a gradient. On the treatment liquid level, therefore, the organic solvent is pulled strongly by the treatment liquid level that contains no organic solvent. Thus, the organic solvent quickly diffuses onto the whole treatment liquid level, whereupon the film is formed containing the organic solvent. This film that contains the organic solvent is referred to as the organic solvent film herein.
The lower the treatment liquid temperature and the larger the temperature difference between the treatment liquid and the organic solvent, the greater the gradient of the surface tension is. The greater the surface tension gradient, the faster the organic solvent diffuses to form the thin organic solvent film with a uniform thickness. The organic solvent film, formed on the treatment liquid level in this manner, serves to prevent the organic solvent vapor from diffusing into the treatment liquid thereunder if the vapor supplied to the space over it is condensed by touching it. Thus, the treatment liquid below the film can be recovered and re-treated to be reused.
In a drying apparatus described in Jpn. Pat. Appln. KOKOKU Publication No. 6-103686, the treatment liquid used is kept at a relatively high temperature substantially equal to that of the organic solvent vapor. A drying fluid layer (layer of a mixture of the treatment liquid and the organic solvent) is formed over the treatment liquid as the organic solvent vapor is fed onto the surface of the treatment liquid. In this case, there is a small temperature difference between the treatment liquid and the organic solvent, and besides, the organic solvent cannot be supplied in plenty in a moment. Accordingly, the thin uniform film of the organic solvent cannot be formed. If the vapor or mist of the organic solvent is supplied to the space over the treatment liquid without forming the organic solvent film on the liquid level, therefore, the organic solvent inevitably diffuses into the treatment liquid without limitation.
In order to form the organic solvent film on the treatment liquid level, the drying apparatus of the present invention is provided with the organic solvent diffusing means for giving the temperature difference not smaller than the predetermined value between the treatment liquid and the organic solvent and feeding the heated organic solvent in the given or larger quantity onto the treatment liquid in a moment.
As the to-be-dried object in the drying vessel passes through the organic solvent film, the organic solvent adheres substantially uniformly to the surface of the object. Since the organic solvent vapor continues to be fed into the drying vessel, it goes on being condensed on the organic solvent film. Thus, the organic solvent film can maintain its stability without being torn.
The drying apparatus of the invention may be provided with a second inert gas supplier for introducing an inert gas into the organic solvent stored in the organic solvent tank. According to this drying apparatus, the organic solvent vapor in the organic solvent tank is diluted with the inert gas. Accordingly, the consumption of the organic solvent used in a drying process can be lowered, and the cost of the drying process can be restricted. Since the volume of the vapor that contains the organic solvent increases, moreover, the sufficient organic solvent vapor in the drying vessel can be secured to cover the to-be-dried object if much of the vapor is condensed on the surface of the object.
The drying apparatus of the invention may be provided with a holding member for holding the to-be-dried object in the drying vessel and a lifter that supports the object for up-and-down motion in the drying vessel. The lifter is raised when the liquid level is lowered to the level of the middle portion of the to-be-dried object as the treatment liquid feeder-discharger discharges the treatment liquid from the drying vessel. By doing this, the object can be separated from the holding member. As the treatment liquid is discharged from the drying vessel, the drying apparatus can prevent the liquid from remaining in the area of contact between the to-be-dried object and the holding member. Thus, production of watermarks can be prevented more securely.
The xe2x80x9cinert gasxe2x80x9d described herein may be any of gases that are chemically inactive and react to no organic solvent, such as argon, helium and other rare gas elements, as well as nitrogen. The xe2x80x9cpure waterxe2x80x9d is water in which the contents of dust and other contamination are minimized.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.